Scientists are getting close to proving what yogis have held to be true for centuries — yoga and meditation can ward off stress and disease.

John Denninger, a psychiatrist at Harvard Medical School, is leading a five-year study on how the ancient practices affect genes and brain activity in the chronically stressed. His latest work follows a study he and others published earlier this year showing how so-called mind-body techniques can switch on and off some genes linked to stress and immune function.

While hundreds of studies have been conducted on the mental health benefits of yoga and meditation, they have tended to rely on blunt tools like participant questionnaires, as well as heart rate and blood pressure monitoring . Only recently have neuro-imaging and genomics technology used in Denninger's latest studies allowed scientists to measure physiological changes in greater detail.

"There is a true biological effect," said Denninger, director of research at the Benson-Henry Institute for Mind Body Medicine at Massachusetts General Hospital, one of Harvard Medical School's teaching hospitals. "The kinds of things that happen when you meditate do have effects throughout the body, not just in the brain."

The government-funded study may persuade more doctors to try an alternative route for tackling the source of a myriad of modern ailments. Stressinduced conditions can include everything from hypertension and infertility to depression and even the aging process. They account for 60 to 90% of doctor's visits in the US, according to the Benson-Henry Institute. The World Health Organization estimates stress costs US companies at least $300 billion a year through absenteeism, turn-over and low productivity.

Denninger's study, to conclude in 2015 with about $3.3 million in funding from the National Institutes of Health, tracks 210 healthy subjects with high levels of reported chronic stress for six months. Unlike earlier studies, this one is the first to focus on participants with high levels of stress. The study published in May in the medical journal PloS One showed that one session of relaxation-response practice was enough to enhance the expression of genes involved in energy metabolism and insulin secretion and reduce expression of genes linked to inflammatory response and stress. There was an effect even among novices who had never practised before.

In a study published last year, scientists at the University of California at Los Angeles and Nobel Prize winner Elizabeth Blackburn found that 12 minutes of daily yoga meditation for eight weeks increased telomerase activity by 43 percent, suggesting an improvement in stress-induced aging.